In the processing of semiconductor workpieces or substrates into integrated circuits excited gas plasmas are often utilized. One such plasma processing method is sputter etching which is used to remove a layer of unwanted material from the substrate surface. The process of sputter etching is generally known and utilizes ionized particles of the charged gas plasma to bombard the surface of a substrate and dislodge or "sputter" away other substrate particles from the surface of the substrate.
In plasma sputter etching, a plasma gas is typically introduced into the processing space of a processing chamber. The processing chamber is preferably vacuum sealed and may be typically fabricated from quartz or another suitable dielectric material. The substrate to be etched is supported on an electrically charged base or electrode within the processing chamber whereon the substrate develops an electrical charge or bias. The plasma gas is introduced into the chamber opposite the surface of the charged substrate, and energy is coupled to the gas through the processing chamber, such as by using an inductive coil which surrounds the processing chamber. The energy from the induced electric field of the coil ionizes the gas particles so that they acquire a net charge that is of opposite polarity to the charge of the substrate support and substrate, and collectively form a gas plasma or plasma cloud. Since the charge of the ionized particles of the plasma and the charge of the substrate are of opposite polarities, the ionized particles in the plasma are attracted to the substrate surface, bombarding the surface and dislodging material particles to etch the wafer surface.
One significant drawback to sputter etching is that the etched material sometimes appears back on the substrate, contaminating the surface and the IC devices formed thereon. More specifically, the material which is etched away from the substrate surface generally deposits on the interior surfaces and walls of the processing chamber. During the process of sputter etching, the processing chamber heats up to a processing temperature due to the energy within the excited plasma and the bombardment and etching of the substrate. After completion of the etching, the inductively coupled energy to the generated plasma is interrupted and the plasma is extinguished. The processing chamber then cools down to the ambient room temperature. The resulting range of the temperature swing between processing and ambience may be approximately 80.degree.-180.degree. C., depending upon the process and the chamber geometry. The wide temperature variation of the processing chamber adversely affects the adhesion of the sputter etched material to the interior surfaces and walls of the processing chamber. The temperature variation of typical plasma processing chamber deteriorates the binding forces between the interior chamber surface and the deposited material, which is typically SiO.sub.2 or another oxide, and between the adjacent layers of the wall deposition. The deterioration of the binding forces creates flaking or peeling of etched material pieces from the walls. The flaked pieces travel back to the substrate and produce irreversible damage through particle contamination of the substrate surface,
The contamination limits the process yield and performance of the plasma processing chamber and decreases the effective lifetime of the processing chamber. Furthermore, the particle contamination reduces the overall productivity of the sputter etching process and increases the cost of the process,
Accordingly, it is an objective of the present invention to reduce contamination in a plasma sputtering etching process. It is a further objective to reduce particle contamination by reducing or eliminating the peeling of etched material pieces from the interior walls of the processing chamber.
It is an additional objective of the present invention to improve the performance of the sputter etching process and to increase the effective yield and throughput of substrates in a plasma sputter etching system. Furthermore, it is an objective to increase the effective life of a sputter processing chamber and to increase the overall productivity of a plasma sputter etching system while reducing operational costs.